Extracardiac conduits in the form of biological or synthetic tubes are known to be used in cardiac surgery, primarily for the correction of ventricular outflow abnormalities in patients. It is also known in the literature that aorta or pulmonary valves, of human or animal origin, can be used for the replacement of defective cardiac valves. Replacement valves have also been made from pericardium.
For example in Ann. Thorac. Surg. 1995, 60, S200, there is described a method of making a valved conduit from pericardium tissue. The tissue is moulded by folding it over a template, and partially fixing it with glutaraldehyde. The template contains raised areas on both surfaces, which during fixation of the tissue, form protuberances on the outer surface of the tissue, so that when the folded tissue is sutured together, these protuberances form sinuses and cusps. The template is removed and the folded tissue sutured together in such a manner as to form cusps on one side of the tissue layer and sinuses on the other. The tissue is then rolled around an axis perpendicular to the fold line and sutured together to form a tubular structure, so that the cusps are on the inside and form a valve. The conduit is finally fixed with glutaraldehyde. However, since the tissue is sewn together to form the cusps after the template is removed, the cusps and sinuses may be irregular in size and shape. Thus may result in the valve not closing completely when the conduit is formed.
Another method of forming sinuses on a conduit, is by applying pressure to the inside of a conduit, which is surrounded by an external stent, so as to stretch the walls radially outwards through the stent, thus generating protuberances in the walls of the conduit. However, this is not a favourable method of forming sinuses, as the walls of the sinuses tend to be thinner and thus weaker than the main wall of the conduit.
It is believed that the exact shape and configuration of the cusps is important to guard against unnatural distortion of the valve in use, which would impair proper sealing of the valve cusps.